Air powered vacuum pump



May 26, 1970 H. L. woon AIR POWERED VACUUM PUMP 3 Sheets-Sheet l Howard L. Wood 1 N VENTOR.

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Q M 9m 3 Sheets-Sheet 5 H. L. WOOD AIR POWERED VACUUM PUMP vQ v8 NQ mi 9Q mQ May 26, 1970 Filed July 9, 1968 Howard L. Wood INVENTOR.

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United States Patent 3,514,226 AIR POWERED VACUUM PUMP Howard L. Wood, Wolf Point, Mont., assignor to Woods Powr-Grip Co., Inc., a corporation of Montana Filed July 9, 1968, Ser. No. 743,341 Int. Cl. F04b 17/00, 19/02 US. Cl. 103-50 '15 Claims ABSTRACT OF THE DISCLOSURE A piston assembly is reciprocated within a vacuum pump housing to produce a vacuum pressure in a suction chamber having a one-Way intake valve. Air under pressure is admitted through a control valve assembly for effecting movement of the piston assembly. A reversal in movement at the ends of the piston stroke is produced by a snap action valve actuator operating through the valve assembly to control the flow of air under pressure to the piston assembly.

This invention relates to vacuum pumps of the fluid pressure operated, reciprocating piston type.

Fluid pressure operated piston pumps and the operating principles associated therewith are well known. Generally, such pumps employ hollow piston enclosing actuating chambers of varying volume on either side of a partition to which fluid under pressure is supplied in order to cause reciprocating movement of the piston within a pump housing. A suction chamber is enclosed within the housing and a vacuum pressure is produced therein dur ing expansion of the suction chamber by movement of the piston assembly in one direction. It is an important object of the present invention to provide a fluid operated vacuum pump of the foregoing type which is of novel construction and arrangement and possesses certain operating attributes which account for unexpected efficiency, operational versatility and economical manufacture, repair and maintenance.

In accordance with the present invention, the pump housing is provided with a one-way intake valve at one axial end featuring a thin disc having a flexible flap portion opened against the bias of its own elasticity and that of a porous, foam-type pad forming a cushion for the piston. Mounted at the other end of the pump housing is a valve assembly through which the flow of air under pressure is controlled in order to effect reciprocatory movement of the piston assembly within the pump housing. The valve assembly is of economical design in that a perfectly cylindrical valve plunger and valve bore are utilized with sealing elements axially spaced apart by rigid spacers to partition the vave bore into separate valve chambers through which air under pressure is conducted to opposite sides of a partitioning structure within the piston assembly enclosing opposed actuating chambers.

A snap-action valve actuator shifts the valve assembly from one position to another as the piston assembly approaches the ends of its stroke in order to abruptly switch the flow of air under pressure from one actuating chamber to the other in order to reverse movement of the piston.

Because of the snap action operation and construction of the control valve assembly, exceptionally efiicient vacuum pump operation is obtained under high pressure loading. Furthermore, the vacuum pump is capable of having two different modes of operation including one in which the pump stops when a predetermined vacuum pressure is attained within the suction chamber, the other mode of operation involving a continuous pumping action Where the force exerted on the piston exceeds the 3,514,226 Patented May 26, 1970 load produced thereon under maximum vacuum within the suction chamber.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIG. 1 is a side elevational view of the vacuum pump with parts broken away and shown in section.

FIG. 2 is a side sectional View through the vacuum pump taken substantially through a plane indicated by section line 2-2 in FIG. 1.

FIG. 3 is an enlarged partial sectional view of the vacuum pump shown in one operational phase.

FIG. 4 is a fragmentary sectional view showing the piston assembly of the vacuum pump in another operational phase.

FIG. 5 is a transverse sectional view with a part broken away and shown in section taken substantially through a plane indicated by section line 5-5 in FIG. 2.

FIG. 6 is a transverse sectional view taken substantially through a plane indicated by section line 6-6 in FIG. 2.

FIG. 7 is a fragmentary sectional view of a portion of the vacuum pump as illustrated in FIG. 1 but in a different operational phase.

FIG. 8 is an enlarged sectional view of a portion of the vacuum pump showing the control valve assembly in one operative position corresponding to the operational phase of the vacuum pump as illustrated in FIG. 3.

FIG. 9 is an enlarged sectional view of the control valve assembly shown in its other operative position.

FIG. 10 is a partial transverse sectional view taken substantially through a plane indicated by section line Ill-10 in FIG. 8.

FIG. 11 is a perspective view of one of the spacer members associated with the control valve assembly.

Referring now to the drawings in detail, and initially to FIGS. 1 and 2, the vacuum pump generally denoted by reference numeral 10 is adapted to be connected to any suitable source of fluid under pressure through a fluid supply conduit 12 connected to the vacuum pump adjacent one end by means of an inlet fitting 14. When so connected to the source of pressurized air or other suitable fluid, the pump is operative to produce a suction pressure adapted to be utilized for any desired purpose by a flexible hose connection at the hose coupling projection 16 extending from an end cap 18 threadedly connected to one axial end of a cylindrical pump housing 20. The end cap 18 thus closes one axial end of the pump housing opposite the axial end closed by a control valve assembly 22 on which the inlet fitting 14 is mounted. Fluid under pressure is admitted through the control valve assembly 22 to the interior of the pump housing through a stationary conduit structure generally referred to by reference numeral 24 on which a piston assembly 26 is slidably mounted for reciprocatory movement. A suction chamber 28 of variable volume is enclosed within the pump housing between the end cap 18 and one side of the piston assembly 26. Thus, a vacuum pressure is produced within the chamber 28 while it is being volumetrically expanded during movement of the piston in one direction under a force exerted thereon by the pressure of the compressed air supplied to the interior of the piston assembly. As the suction chamber 28 is ex panding air is exhausted from the vent chamber 30 on the other side of the piston assembly through vent openings 32 formed in the closure cap formation 34 associated with the control valve assembly 22. As a result of the vacuum pressure produced within the suction chamber 28, air enters the suction chamber through an intake passage 36 centrally formed within the end cap 18 and through a normally closed one-way or check valve assembly 38 mounted on the inside of the end cap 18.

As more clearly seen in FIGS. 3 and 5, the one-way valve assembly 38 consists of a thin metallic disc 40 secured or cemented to the end cap and having an elastically flexible flap portion 42 normally closing the inner end of the intake passage 36. A cushion pad 44 made of a porous, foam type material is cemented to the disc 40 and includes a central portion 46 which is deflectable by the flap portion 42 of the disc when opened by the inflow of air as shown in FIG. 3. Thus, the one-way valve 38 will be opened as illustrated when a vacuum pressure of suflicient degree is produced within the suction chamber 28 exceeding the closing bias exerted on the valve assembly by the elastic restoring force of the flap portion 42 as well as that of a reinforcing spring element 48 which may be embedded within the cushion pad. The closing bias of the one-way valve is of course overcome when a minimum vacuum pressure is developed within the suction chamber 28 during the suction stroke of the piston assembly 26. The valve will of course be closed during the return stroke of the piston assembly when the pressure within the suction chamber 28 is equal to or above atmospheric pressure.

The piston assembly as more clearly seen in FIGS. 2 and 3, includes an axially elongated tubular member 50 closed at one end by an apertured end cap 52 through which the conduit structure 24 extends. An annular, cupshaped flexible sealing element 54 is mounted in abutting relation to the end cap 52 in wiping engagement with the external surface of the conduit structure so as to maintain the interior of the tubular member 26 pressure sealed. The axial end of the tubular member 50 opposite the end cap 52 is closed by a relatively rigid backing disc member 56 having an internally threaded collar portion 58 threaded onto the end portion of the tubular member 50. The collar portion constitutes a radially inner retainer for an annular sealing element 60 made of a flexible material such as rubber. The radially outer flange portion 62 of the flexible sealing element 60 is in wiping engagement with the internal cylindrical surface of the pump housing while the radially inner, perforated disc portion 64 abuts the backing disc member 56. It will be apparent therefore, that during movement of the piston assembly in a right hand direction as viewed in FIG. 3, the vacuum pressure developed within suction chamber 28 and the above atmopsheric pressure within the vent chamber 30 will hold the sealing element 60 in abutment with the backing disc member 56 and in wiping engagement with the pump housing for effective development of a relatively high vacuum pressure within the chamber 28. During the return stroke of the piston assembly in a left hand direction, the increase in pressure within the chamber 28 due to closing of the one-way valve assembly 38 will cause deflection of the sealing element 60 as illustrated in FIG. 4 permitting leakage flow of air through the openings 66 in the sealing element and between its sealing flange portion 62 and the internal surface of the pump housing. Thus, the piston assembly may move to the end of its return stroke under a reduced loading until it abuts the cushion pad 44 of the one-way valve assembly.

The piston assembly is supportingly guided for reciprocatory movement within the pump housing 20 by means of the conduit structure 24 which also establishes a pair of volumetrically variable actuating chambers 68 and 70 on opposite sides of a stationary partition assembly 72 associated with the conduit structure. The conduit structure includes an outer cylindrical conduit member 74 secured to and extending from the valve assembly 22 into the pump housing in substantially concentric relation thereto. An inner conduit member 76 is also connected to the valve assembly and extends concentrically through the outer conduit member terminating 4 in an externally threaded end portion on which an assembly nut 78 is mounted for holding the partition assembly 72 in an axially fixed position against the collar 80 on the outer conduit member 74. The partition assembly includes a rigid backing disc 82 held on the inner conduit member 76 abutting the end of the outer conduit member 74 as more clearly seen in FIG. 3. The backing disc 82 is spaced from the assembly nut 78 by a spacing sleeve 84 on which a flexible sealing element 86 is mounted for wiping engagement with the tubular piston member 50 on one side of the backing disc 82. A flexible sealing element 88 is disposed on the outer conduit member 74 between the backing disc 82 and the collar 80. A radially inner passage 90 extends through the inner conduit member 76 for communication with the actuating chamber 68 while a radially outer annular passage 92 surrounding the inner conduit member extends through the outer conduit member for communication with the actuating chamber 70. Accordingly, a port 94 is formed in the collar 80 to establish communication between the passage 92 and the chamber 70, the passage 92 being closed by the spacer 96 at the end of the outer conduit member as shown in FIG. 3. Thus, fluid under pressure supplied to the chamber 70 through passage 92 as shown in FIG. 3 will pressurize chamber 70 causing movement of the piston assembly 26 in a right hand direction. Chamber 68 will therefore be volumetrically contracted in this phase of operation with the air therein being vented through passage 90 into the vented chamber 30 of the piston housing through the valve assembly 22. For movement of the piston in the left hand direction, fluid under pressure is supplied to the chamber 68 through passage 90 while fluid within chamber 70 is vented through passage 92 causing flow of air in directions opposite to those indicated by the arrows in FIG. 3. Thus, the control valve assembly 22 is operative to abruptly reverse flow through the passages 90 and 92 at the ends of the piston stroke.

Referring now to FIGS. 8 and 10, it will be observed that the control valve assembly 22 includes a valve body 98 to which the inlet fitting 14 is threadedly connected for establishing fluid communication between the source of compressed air and the inlet passage 100 formed within the valve body in intersecting relation to a cylindrical valve bore 102 disposed in parallel spaced relation to the longitudinal axis of the pump housing 20 to which the valve body 98 is threadedly connected by the end cap formation 34. The valve bore includes a diametrically enlarged threaded end portion 104 threadedly receiving a hollow closure plug 106 having a flange portion 108 abutting the valve body and provided with an internal cavity 110 closed by a threaded plug 112 forming a stop adapted to be abutted by the head 114 connected to one end of a cylindrical valve plunger 116 slidably received through an aperture in the hollow closure plug 106 aligned with an opening 118 in the valve body communicating with the valve bore 102 at an axial end opposite the closure plug 106. The valve plunger is provided intermediate its opposite ends, with a plurality of angularly spaced arcuate slots 120 and 122 at axially spaced locations in order to establish fluid communication between spaced valve chambers in the different operative positions of the valve plunger.

Valve chambers 124, 126 and 128 are separated from each other within the valve bore 102 by means of annular, cup-shaped, flexible sealing elements 130 engaged with five relatively rigid spacers on either side of each sealing element in the illustrated embodiment consisting of two spacers 132, two spacers 134 and one spacer 136. Each of the spacers includes a perforated tubular portion such as the tubular portion 138 of the spacer 134 as shown in FIG. 11. An annular flange 140 is connected to one end of the perforated tubular portion in the case of the spacers 132 and 134. The spacers 132 differ from the spacers 134 in that the tubular portions are of different axial lengths. The spacer 136 on the other hand does not have any flange portions at either axial end and is therefore received within the cup-shaped formation of a pair of oppositely facing sealing elements 1 30 to form the central valve chamber 126 with which the inlet passage 100 communicates. The sealing elements 130 on either axial side of the spacer 136 are backed by the flange portions 140 of the spacers 134 which engage sealing elements backed by the flange portions of the end spacers 132 which respectively abut the valve body at one end and the closure plug 106 at the other end of the valve bore. Thus, the sealing elements and spacers seal the valve chambers 124 and 128 on either side of the central valve chamber 126 in an eflicient and economical manner since the valve plunger may be made from perfectly cylindrical stock and the valve bore formed by economical manufacturing methods. The spacers fixedly space the sealing elements 130 from each other and are radially spaced from the valve plunger so as to engage and back the sealing elements to assure effective pressure sealing.

While the central valve chamber 126 communicates with the inlet passage 100, valve chamber 124 communicates with the conduit passage 92 through connecting passage 142 formed in the valve body in axially spaced relation to the inlet passage 100 on the side of the valve bore 102 opposite the inlet passage. The connecting passage 142 is closed on the side of the outer conduit member 74 by the threaded plug 144 while a second threaded plug 146 closes a second connecting passage 148 establishing communication between the valve chamber 128 and the inner conduit passage 90. The valve spaces at the opposite axial ends of the valve bore 102 are vented through the vent chamber 30 within the pump housing to which the valve spaces are connected by passages 150 and 152 formed in the valve block 98 as shown by dotted lines in FIGS. 8 and 9. In one operative position of the valve plunger with the head 114 abutting the stop plug 112 as shown in FIG. 8, communication is established between the valve chamber 128 and the vented spaces at one end of the valve bore by means of the slots 122. Accordingly, the conduit passage 90 will be in fluid communication with the vented chamber 30. In this same position of the valve plunger, the slots 120 establish fluid communication between the valve chamber 126 and the valve chamher 124 to thereby form a fluid connection between the inlet passage 100 and the outer conduit passage 92. Accordingly, the actuating chamber 70 is pressurized to cause advancement of the piston assembly in a working direction. When the valve plunger 116 is displaced to its other operative position as shown in FIG. 9 with the head 114 abutting the inner end of the closure plug 106, the slots 122 establish fluid communication between the pressurized valve chamber 126 and the valve chamber 128 communicating with the inner conduit passage 90 to thereby pressurize the actuating chamber 68 within the piston assembly. The chamber 70 at this time is vented through the outer conduit passage 92 which communicates through connecting passage 142, valve chamber 124 and slots 120 with the vented space at one end of the valve bore communicating through passage 150 with the vented chamber 30. It will be apparent therefore, that a reversal in movement of the piston assembly will be effected by shifting the valve plunger 116 between the two operative positions thereof as respectively shown in FIGS. 8 and 9.

Abrupt shifting of the valve plunger 116 is effected as the piston assembly approaches the opposite ends of its stroke by means of a snap action actuator mechanism 153 connected to that end of the valve plunger projecting into the pump housing as more clearly seen in FIG. 1. The actuator 153 includes a spring follower member having a pair of force transmitting arms 154 interconnected in laterally spaced relation to each other on either side of the axis of the valve plunger 116 by a U-shaped connecting portion 156 held in a slot 158 of the valve plunger by a retainer clip 160. A pair of follower rollers 162 are rotatably mounted at the ends of the spring arms 154. The follower rollers are engaged with a longitudinal cam member 164 projecting from the side of the tubular member 50 of the piston assembly. Intermediate the ends of the piston assembly stroke, the cam member holds the force transmitting spring arms 154 laterally spaced apart against their spring bias. The cam member is accordingly provided with a pair of parallel spaced cam profile portions 166 which are substantially parallel to the longitudinal axis of the pump housing 20 and the path of movement of the piston assembly so that no longitudinal force will be transmitted to the spring arms 154 through the rollers 162 during a major portion of the piston assembly movement. The cam member is also provided with oppositely converging profile portions 168 at the opposite longitudinal ends thereof engaged by the follower rollers 162 as the piston assembly approaches opposite ends of its stroke. In view of the convergence of the end profile portions 168 of the cam member, a longitudinal force component is transmitted through the spring arms 154 when the follower rollers 162 engage the end profile portions. Also, since the end profile portions 168 converge in opposite directions at the opposite ends of the cam member, the longitudinal force components transmitted to the spring arms will be in opposite directions. It will therefore be apparent, that as the piston assembly approaches the end of its suction stroke in a right hand direction, a longitudinal force component in a left hand direction will be transmitted through the spring arms 154 in view of the spring bias of the spring arms urging the rollers 162 toward each other. This longitudinal force component is transmitted to the valve plunger 116 causing it to shift in a left hand direction in order to move the valve plunger to the position illustrated in FIG. 9. A reversal in movement of the piston assembly is thereby effected as hereinbefore indicated, causing the piston to begin movement in a return stroke direction. As the piston assembly approaches the end of its return stroke, a longitudinal force component is transmitted to the spring arms 154 in a right hand direction as illustrated in FIG. 7 causing the valve plunger 116 to shift to the position illustrated in FIG. 8 to again cause a reversal in movement of the piston assembly. Thus, the actuating mechanism 153 automatically and abruptly reverses movement of the piston assembly as it approaches the ends of its stroke. In order to insure that the follower rollers 162 are not displaced from the cam profile portions of the cam member, they are provided with grooves 170 as more clearly seen in FIG. 6 matching the cross-sectional profile formations on the cam member.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

What is claimed as new is as follows:

1. A vacuum pump powered by a source of fluid under pressure comprising an elongated pump housing having opposite ends, suction valve means closing one of said opposite ends of the housing, a control valve assembly connected to said source and closing the other of the ends of the housing, conduit means supported by said control valve assembly extending therefrom into the housing, piston means slidably mounted on the conduit means within the housing for establishing an expansible suction chamber to which the suction valve means is exposed, and snap-action actuating means engageable by the piston means and connected to the valve assembly for controlling flow of the fluid from the source through the conduit means to effect reciprocation of the piston means.

2. A vacuum pump powered by a source of fluid under pressure comprising an elongated pump housing having opposite ends, suction valve means closing one of said opposite ends of the housing, a control valve assembly connected to said source and closing the other of the ends of the housing, conduit means supported by said control valve assembly extending therefrom into the housing, piston means slidably mounted on the conduit means within the housing for establishing an expansible suction chamber to which the suction valve means is exposed, and snap-action actuating means engageable by the piston means and connected to the valve assembly for controlling flow of the fluid from the source through the conduit means to effect reciprocation of the piston means, said piston means comprising a tubular member slidably supported on the conduit means, a rigid backing element secured to the tubular member at one axial end forming an annular, flow restrictive gap within the housing in communication with the suction chamber, and a flexible sealing element mounted on the tubular member having a radially outer sealing portion in wiping engagement with the housing and a radially inner perforated portion in engagement with the backing element during movement of the piston means in one direction.

3. The combination of claim 2 wherein said conduit means comprises a pair of susbtantially concentric tubes forming a pair of flow passages extending between the valve assembly and the piston means, a partition element fixedly mounted on said tubes adjacent an end opposite the valve assembly, said partition element including sealing means wipingly engaged with the piston means for internally partitioning the same into actuating chambers respectively communicating with said pair of flow passages, said actuating chambers being enclosed on opposite sides of the partition element by the tubular member.

4. The combination of claim 3 wherein said suction valve means comprises an end cap connected to the housing having an intake opening therein, a disc mounted on the end cap having a flap portion closing the opening in the end cap, and a cushion pad of porous material mounted on the disc adapted to be engaged by the piston means at one end of a stroke.

5. The combination of claim 4 wherein said actuating means comprises an actuating rod connected to the valve assembly for longitudinal movement substantially parallel to the piston means, a pair of force transmitting spring arms connected to the actuating rod in spaced relation to each other, cam means mounted on the piston means in engagement with the spring arms for holding the same in spaced relation to each other against a spring bias, said cam means having spaced portions transforming said spring bias into axial force components in opposite directions as the piston means approaches opposite ends of a stroke.

6. The combination of claim 5 wherein said valve assembly includes a valve body having a cylindrical bore, a cylindrical valve plunger connected to the actuating means, means mounting the valve plunger for axial movement within the bore, a plurality of annular sealing elements wipingly engaged with the valve plunger within the bore partitioning the same into axially spaced valve chambers, and spacer means engaging said sealing elements for holding the same in fixed axially spaced relation to each other, said valve plunger being provided with axially extending slots bridging selected ones of said valve chambers upon axial displacement of the valve plunger by the actuating means.

7. The combination of claim -6 wherein said spacer means comprises a plurality of rigid members, each rigid member having a perforated tubular portion engaging one of the sealing elements at one axial end thereof in radially spaced relation to the valve plunger and a flange portion at the other axial end of the tubular portion of some of the rigid members abutting another of the sealing elements to form a backing therefor.

8. A vacuum pump powered by a source of fluid under pressure comprising an elongated pump housing having opposite ends, suction valve means closing one of said opposite ends of the housing, a control valve assembly connected to said source and closing the other of the ends of the housing, conduit means supported by said control valve assembly extending therefrom into the housing, piston means slidably mounted on the conduit means within the housing for establishing an expansible suction chamber to which the suction valve means is exposed, and snap-action actuating means engageable by the piston means and connected to the valve assembly for controlling flow of the fluid from the source through the conduit means to effect reciprocation of the piston means, said suction valve means comprising an end cap connected to the housing having an intake opening there in, a disc mounted on the end cap having a flap portion closing the opening in the end cap, and a cushion pad of porous material mounted on the disc adapted to be engaged by the piston means at one end of a stroke.

9. A vacuum pump powered by a source of fluid under pressure comprising an elongated pump housing having opposite ends, suction valve means closing one of said opposite ends of the housing, a control valve assembly connected to said source and closing the other of the ends of the housing, conduit means supported by said control valve assembly extending therefrom into the housing, piston means slidably mounted on the conduit means within the housing for establishing an expansible suction chamber to which the suction valve means is exposed, and snap-action actuating means engageable by the piston means and connected to the valve assembly for controlling flow of the fluid from the source through the conduit means to effect reciprocation of the piston means, said actuating means comprising an actuating rod connected to the valve assembly for longitudinal movement substantially parallel to the piston means, a pair of force transmitting spring arms connected to the actuating rod in spaced relation to each other, cam means mounted on the piston means in engagement with the spring arms for holding the same in spaced relation to each other against a spring bias, said cam means having spaced portions transforming said spring bias into axial force components in opposite directions as the piston means approaches opposite ends of a stroke.

10. The combination of claim 9 wherein said valve assembly includes a valve body having a cylindrical bore, a cylindrical valve plunger connected to the actuating means, means mounting the valve plunger for axial movement within the bore, a plurality of annular sealing elements wipingly engaged with the valve plunger within the bore partitioning the same into axially spaced valve chambers, and spacer means engaging said sealing elements for holding the same in fixed axially spaced relation to each other, said valve plunger being provided with axially extending slots bridging selected ones of said valve chambers upon axial displacement of the valve plunger by the actuating means.

11. The combination of claim 10 wherein said spacer means comprises a plurality of rigid members, each rigid member having a perforated tubular portion engaging one of the sealing elements at one axial end thereof in radially spaced relation to the valve plunger and a flange portion at the other axial end of the tubular portion of some of the rigid members abutting another of the sealing elements to form a backing therefor.

12. A vacuum pump powered by a source of fluid under pressure comprising an elongated pump housing having opposite ends, suction valve means closing one of said opposite ends of the housing, a control valve assembly connected to said source and closing the other of the ends of the housing, conduit means supported by said control valve assembly extending therefrom into the housing, piston means slidably mounted on the conduit means within the housing for establishing an expansible suction chamber to which the suction valve means is exposed, and snapaction actuating means engageable by the piston means and connected to the valve assembly for controlling flow of the fluid from the source through the conduit means to effect reciprocation of the piston means, wherein said valve assembly including a valve body having a cylindrical bore, a cylindrical valve plunger connected to the actuating means, means mounting the valve plunger for axial movement within the bore, a plurality of annular sealing elements wipingly engaged with the valve plunger within the bore partitioning the same into axially spaced valve chambers, and spacer means engaging said sealing elements for holding the same in fixed axially spaced relation to each other, said valve plunger being provided with axially extending slots bridging selected ones of said valve chambers upon axial displacement of the valve plunger by the actuating means.

13. The combination of claim 12 wherein said spacer means comprises a plurality of rigid members, each rigid member having a perforated tubular portion engaging one of the sealing elements at one axial end thereof in radially spaced relation to the valve plunger and a flange portion at the other axial end of the tubular portion of some of the rigid members abutting another of the sealing elements to form a backing therefor.

14. In combination, a vacuum pump mechanism having fluid displacing means and a housing, and a control valve assembly comprising a valve body mounted on the housing and having a cylindrical bore, a cylindrical valve plunger connected to the fluid displacing means, means mounting the valve plunger for axial movement within the bore, a plurality of annular sealing elements wipingly engaged with the valve plunger Within the bore partitioning the same into axially spaced valve chambers, and spacer means engaging said sealing elements for holding the same in fixed axially spaced relation to each other, said valve plunger being provided with axially extending slots bridging selected ones of said valve chambers upon axial displacement of the valve plunger by the fluid displacing means.

15. The combination of claim 14 wherein said spacer means comprises a plurality of rigid members, each rigid member having a perforated tubular portion engaging one of the sealing elements at one axial end thereof in radially spaced relation to the valve stem and a flange portion at the other axial end of the tubular portion of some of the rigid members abuting another of the sealing elements to form a backing therefor.

References Cited UNITED STATES PATENTS 2,162,144 6/1939 Waugh 10350 2,596,360 5/1952 Blakeway 1035O XR 3,152,016 10/1964 Drushella 103--158 XR ROBERT M. WALKER, Primary Examiner US. Cl. X.R. 

